PEOPLE are fascinated by the prospect of life in space. My
proof? I count an even dozen volumes on bioastronomy on my bookshelf,
all published with the past year. But among these, Stuart Clark's Life
On Other Worlds and How To Find It is unique in its approach. We must
walk before we run, says Clark. Don't even ask the age-old question
"Are we alone?" until you've brushed up on the basics.

And these basics are the principles and assumptions that underlie
any search for life beyond our sphere. Here, Clark invokes the
writings of Carl Sagan, Paul Davies, David Blair, Christian de Duve
and many other respected experts. A swift tutorial on cosmic evolution
plus a smattering of basic thermodynamics takes us from the big bang
to the formation of planets that might, just possibly, support life.
This sets the stage for a lucid discussion of the emergence of life
and exactly what constitutes a hospitable environment. The backdrop is
a picture of Earth-like planets as commonplace among the myriad worlds
in our Universe.

But just because life could exist elsewhere is no guarantee that it
does. To find out, we have to do the experiment. We have to collect
the data.

The search for life within our own Solar System has its roots in
the 18th-century furore over supposed canals on Mars. Centuries later,
the controversy continues, but now it is over the 1996 claim that a
Martian meteorite contains microbial fossils. Exobiologists have not
rejected the prospect of finding primitive life close to home. Several
space missions are due to leave the drawing board and test for the
presence of life.

Their search has also been given new impetus by the discovery of
planets outside the Solar System, the first detected only five years
ago. All these extrasolar planets are giants like Jupiter, but there
are plans to launch space-based observatories capable of spotting
Earth-sized planets and of identifying atmospheric gases conducive
to--and perhaps even indicative of -- life.

But what will this life be like? Those involved in SETI, the search
for extraterrestrial intelligence, hope to find intelligent,
technologically advanced life rather than brainless bacteria. The more
prevalent intelligence is, the greater will be our opportunity for
contact. Clark has a crack at defining intelligence and pinning down
the role it plays in evolution and survival.

The high spot for fans of SETI science will be the account of our
efforts to communicate with aliens. In 1820, for example, Karl Gauss
proposed creating a giant triangle of trees in Siberia to signal our
mathematical prowess to our supposed lunar neighbours. Recent efforts
have been more sophisticated. Clarke briefly mentions recent attempts to detect alien laser beacons, but, sadly, neglects to mention the pioneering Optical SETI work of british engineer Dr. Stuart Kingsley.

The
problem of defining what constitutes proof is juxtaposed against
public suspicions about hidden evidence and government cover-ups. As a
false alarm recently showed, announcing to the world that we've found
an alien signal may be a problem. And should we fear our Galactic
neighbours? Controversy surrounds active SETI, the deliberate
transmission of messages from Earth, for example.

Which brings us back to the well-worn Fermi paradox: where are
they? Clark is convinced we are not alone. But if the
extraterrestrials won't come to us, perhaps we'll have to go to them.
That's the excuse for an entertaining rummage through the wilder
reaches of technology: fusion rockets, solar sails, matter-antimatter
reaction engines and lunar mining, not to mention self-replicating Van
Neumann probes and instantaneous communication via quantum entangled
particles.

However we find it, Clarke is certain we'll get there somehow--and
that there's an abundance of extraterrestrial life. An astronomy
educator by trade, he uses wit, humour and even the occasional Star
Trek cliché to make his case. But this is not a speculative work, and
Clark's personal conclusions are incidental to his broader picture.
His finale as an eloquent justification for the continuation of
SETI. "Only by the continued efforts and collaboration of the
scientists, who approach the quest from their own unique vantage
points, can we hope to find the answer to this, the most perplexing
question of our existence...is anybody out there?" he writes.

Life On Other Worlds is visually spare, but it is rich in language
and long on clarity. As a SETI professional, I kept a sharp eye out
for any errors. I found only one, and a minor one at that. In
discussing the signal detection hoax of October 1998, Clark says it
was "an amateur radio astronomer who claimed to have picked up a
message from the star EQ Pegasi, just 22 light years away". In fact,
an anonymous Internet hacker, posing as an amateur radio astronomer,
made that claim. The distinction is important, as amateur astronomers
are disciplined and professional.

As an astronomer, Clark is well aware of the significant contributions
of amateurs to his discipline. He speaks well and clearly to the
educated non-scientist in Life On Other Worlds and How To Find It, an
engaging and worthy read. Astronomer Patrick Moore, whose The Sky At
Night is Planet Earth's longest-running television series, writes in
the foreword, "in my view [this book] is the best of its kind that I
have seen, and it will have an honoured place on my shelf."